The present invention relates to novel organosiloxane compositions comprising a platinum group metal hardening catalyst and a ketone compound transitory inhibitor therefor. More especially, this invention relates to organopolysiloxane compositions which are stable for appreciable periods of time at ambient temperature, which period of stability is varied depending upon the field of use to which a given composition is to be put, which compositions harden under appropriate curing conditions (heat treatment, treatment with U.V. or infra-red rays, treatment with ionizing radiation, and the like). This hardening or curing is carried out via the well-known reactions of .tbd.SiH groups with unsaturated olefin radicals bonded to silicon atoms, such reactions being catalyzed by a platinum group metal.
The subject compositions are generally stored before use in the form of two-component or two-pack compositions, the two components being intimately mixed immediately before use to form a single composition, and the principal problem is to avoid premature gelation of such compositions. It is hence necessary that these compositions incorporate a transitory inhibitor for the catalyst, which inhibitor inhibits or retards the catalytic activity at ambient temperature, but whose inhibitory activity disappears at elevated temperatures during the treatment for cross-linking of the compositions.